1. Field of the Invention
The present invention relates to a dielectric ceramic composition and a dielectric device. The dielectric ceramic composition of the present invention particularly is suitable, for example, as a material for a dielectric device used in a high-frequency region such as a microwave band and a millimeter wave band.
2. Description of the Related Art
In recent years, dielectric ceramics have been used widely for dielectric resonators and dielectric filters used in a microwave region and a millimeter wave region. Dielectrics used for such purposes have been required to have a high no-load Q-value (Qu-value), a large dielectric constant (∈r), and a small and arbitrarily variable temperature coefficient (xcfx84f) of a resonance frequency. However, as the dielectric constant of a dielectric ceramic is larger, a dielectric device becomes smaller. Therefore, with an increase in frequency of a communication system, there is an increasing demand for a dielectric ceramic composition with a relatively small dielectric constant in view of improving processing precision and reducing a conductor loss of a dielectric device.
On the other hand, by simultaneously sintering a dielectric ceramic composition and a conductor (e.g., Ag) having a high conductivity, an inexpensive dielectric device can be obtained having a low conductor loss. In order to realize this, there is a demand for a dielectric ceramic composition that can be sintered at 950xc2x0 C. or lower.
As a dielectric ceramic composition with a small dielectric constant, MgTiO3xe2x80x94CaTiO3 ceramics (see JP 6(1994)-92727 A), Al2O3 ceramics, and a ceramic composition obtained by adding a glass composition to an Al2O3 ceramic conventionally are known.
Although the MgTiO3xe2x80x94CaTiO3 ceramic has relatively satisfactory dielectric characteristics, it cannot be sintered at 950xc2x0 C. or lower. The Al2O3 ceramic has a high Qu-value, and a small dielectric constant (∈r) (i.e., about 10); however, it has a large temperature coefficient (xcfx84f) of a resonance frequency, and cannot be sintered at 950xc2x0 C. or lower. The ceramic composition in which a glass composition is added to the Al2O3 ceramic has too large temperature coefficient (xcfx84f) of a resonance frequency.
Therefore, with the foregoing in mind, it is an object of the present invention to provide a dielectric ceramic composition that has a high no-load Q (Qu)-value, a dielectric constant (∈r) of about 10 to 30, and a small absolute value of a temperature coefficient (xcfx84f) of a resonance frequency, and can be sintered at 950xc2x0 C. or lower. It is another object of the present invention to provide an inexpensive dielectric device with a low loss, suitable for use in a high frequency region such as a microwave band and a millimeter band.
In order to achieve the above-mentioned object, a dielectric ceramic composition of the present invention includes a first component and a second component, wherein a content of the second component is in a range of 25 to 80 wt % (weight %). The first component is a complex oxide represented by Formula: xZrO2-yTiO2-zL(1+u)/3M(2xe2x88x92u)/3O2, wherein L is at least one element selected from the group consisting of Mg, Zn, Co, and Mn, M is at least one element selected from the group consisting of Nb and Ta, and x, y, z, and u are values represented by x+y+z=1, 0.10xe2x89xa6xxe2x89xa60.60, 0.20xe2x89xa6yxe2x89xa60.60, 0.01xe2x89xa6zxe2x89xa60.70, and 0xe2x89xa6uxe2x89xa61.90. The second component is a glass composition containing an oxide of at least one element selected from the group consisting of Si, B, Al, Ba, Ca, Sr, Zn, Ti, La, and Nd.
According to the above-mentioned configuration, a dielectric ceramic composition having a high Qu-value, ∈r of about 10 to 30, and xcfx84f with a small absolute value can be obtained. Furthermore, the above-mentioned dielectric ceramic composition can be sintered at a temperature of 950xc2x0 C. or lower. It is preferable that u satisfies 0 less than u. Furthermore, the second component preferably is a glass composition containing Si and B.
In the dielectric ceramic composition of the present invention, a preferable example of the second component is a glass composition containing 30 to 60 wt % of SiO2, 2 to 30 wt % of B2O3, 2 to 10 wt % of Al2O3, and 20 to 50 wt % of QO. Another preferable example of the second component is a glass composition containing 30 to 60 wt % of SiO2, 2 to 10 wt % of B2O3, 2 to 10 wt % of Al2O3, 20 to 50 wt % of QO, and 5 to 15 wt % of La2O3. Still another preferable example of the second component is a glass composition containing 40 to 60 wt % of SiO2, 2 to 10 wt % of B2O3, 2 to 10 wt % of Al2O3, 20 to 50 wt % of QO, and 1 to 5 wt % of ZnO. Still another preferable example of the second component is a glass composition containing 15 to 30 wt % of SiO2, 5 to 20 wt % of BaO, 5 to 15 wt % of RO, 10 to 25 wt % of ZnO, 10 to 30 wt % of TiO2, and 10 to 30 wt % of T2O3. In the above-mentioned second component, Q is at least one element selected from the group consisting of Ba and Ca, R is at least one element selected from the group consisting of Ca and Sr, and T is at least one element selected from the group consisting of La and Nd.
In the dielectric ceramic composition of the present invention, it is preferable that the first component contains, as a main phase, a ZrTiO4 phase in which at least one element selected from the group consisting of Mg, Zn, Co, and Mn and at least one element selected from the group consisting of Nb and Ta are substituted in a solid phase. In the present specification, the term xe2x80x9cmain phasexe2x80x9d refers to a component present in a content of 50 wt % or more. It also is preferable that 0.5xe2x89xa6a/bxe2x89xa61.9 (a is a total of mole fractions of at least one element selected from the group consisting of Mg, Zn, Co, and Mn substituted in a solid phase of ZrTiO4, and b is a total of mole fractions of at least one element selected from the group consisting of Nb and Ta substituted in a solid phase of ZrTiO4) is satisfied in the first component.
A dielectric device of the present invention includes a dielectric ceramic and a conductor formed so as to be in contact with the dielectric ceramic, wherein the dielectric ceramic includes a dielectric ceramic composition of the present invention, and the conductor contains, as a main component, at least one element selected from the group consisting of Ag and Pd. This dielectric device is suitable for use in a high-frequency region such as a microwave band and a millimeter wave band and has a low loss. Furthermore, the dielectric device can be produced at a low cost because the dielectric ceramic and the conductor can be sintered simultaneously.
These and other advantages of the present invention will become apparent to those skilled in the art upon reading and understanding the following detailed description with reference to the accompanying figures.